Influence of Reservoir on Local Climate
The biggest problem encountered by man-made terrain climatology is unpredictability, because the influence of man-made terrain on climate is complicated and interlocking in many aspects. On February 23, 1992, the author wrote the article "It is advisable not to build the Three Gorges Project" (which was submitted to newspapers and failed to be published). The article pointed out that the mega-project is tantamount to a sudden strong impact on the natural environment; Its complex chain reaction and consequences, human beings still lack enough experience to give a reliable prediction in advance. For the Three Gorges Project, it is equivalent to suddenly cutting off the third largest river in the world that has been flowing for tens of millions of years. Obviously, no one is qualified to say that he can foresee all the consequences of this mutation; Even if someone dares to say this, it is an irresponsible boast and cannot be used as a reliable basis for decision-making.
For example, the Three Gorges Project may change the local and nearby geological environment, and the bearing capacity of the earth's crust will change, which may lead to earthquakes or other harmful and beneficial effects. Another example is that the Three Gorges Project may change the local and large-scale climate change, and the flow route and rainfall range of the monsoon may also change accordingly; Arid areas may become rich in rain, but areas with favorable weather may also become water-deficient areas.
it should be pointed out that the unpredictable impact of artificial terrain on climate is largely due to the fact that the academic research on artificial terrain climatology is still in its infancy. With the in-depth study of artificial terrain climatology, the unpredictable effects will gradually decrease and the foreseeable phenomena will gradually increase.
specifically, to deeply and quantitatively study the influence of man-made terrain on climate, we must first solve the problem of parameter measurement. For example, to study the influence of reservoir dam on water vapor transport, it is necessary to measure the water vapor flow in river valleys for a long time before the reservoir dam is built; After the completion of the reservoir dam, the water vapor flow monitoring of the river channel should continue for a long time. Obviously, this is not an easy task, nor can it be completed in a short time. Among them, one of the technical problems involved is how to quickly and accurately measure the water vapor content in low-level air (below 5 meters above sea level or below 5 meters in relative height), including the water content of gaseous water vapor and the water content of liquid water vapor, as well as the flow direction and speed of these water vapor.
Secondly, the corresponding database, high-quality mathematical model of water vapor flow in artificial terrain and its corresponding computer simulation system should be established. There is no doubt that this is also not an easy thing. For example, the wind resistance effect of Xin 'anjiang reservoir dam and the wind resistance effect of Three Gorges reservoir dam are not only related to the physical size of the reservoir dam, but also related to the surrounding environment, so it may be necessary to establish different mathematical models.
The reason is very simple. The influence scope and degree of wind resistance effect of reservoir dams on local climate will be very different in different regions and different geographical backgrounds. Xin 'anjiang Reservoir Dam is located in Zhejiang Province, which is very close to the coastline. Sea breeze and typhoon play a leading role in the flow and distribution of local water vapor. In contrast, the Three Gorges of the Yangtze River is located in the inland of China, and the impact of typhoons is relatively small. The main channel of water vapor transported from the east (coastal areas) to the west (Chongqing and Sichuan basins) is the Three Gorges; Therefore, the construction of the dam in the Three Gorges will inevitably have a relatively greater impact on the water vapor transport in the upper reaches of the Three Gorges Dam.
furthermore, in the summer of 26, Chongqing, eastern Sichuan and other places continued to suffer from high temperature and drought, and the water level in the middle and lower reaches of the Yangtze River and its tributaries continued to fall (this may be a very dangerous signal). Not all of them were influenced by the artificial terrain of the Three Gorges Dam, but they should also be related to the built and under construction reservoir dams in the Nujiang Gorge, Lancang Gorge and Jinshajiang Gorge in Hengduan Mountains, and the latter even played a more important role. The author has written many times that the Sanjiang Gorge in the Hengduan Mountains, which runs north and south, is the throat lifeline of water resources in mainland China. The water vapor from the Indian Ocean to the north passes through the Himalayan Gorge through the Bay of Bengal and enters the Qinghai-Tibet Plateau. One of the most important water vapor channels is the Yarlung Zangbo Grand Canyon and the other is the Hengduan Grand Canyon. In addition, the changes of natural environment (such as Indonesia earthquake and tsunami) and man-made terrain (coastal cities with heat wall effect) in the Indian Ocean region also affect the trend and intensity of atmospheric circulation in the Indian Ocean to a greater or lesser extent. The problem is that we still lack effective means to quantitatively study the relationship between climate change and artificial terrain of the giant system in the above vast areas.
3. Related disciplines involved in artificial terrain climatology
As we all know, the appearance of reservoir dams will not only affect the climate, but also have a series of impacts on the distribution of plants and animals, as well as surface landslides and crustal stress; The above effects are both offset and superimposed, which undoubtedly further increases the research difficulty of artificial terrain climatology. In view of this, to carry out the research of artificial terrain climatology, scholars from various disciplines should be invited to "consult" when necessary, and they should work together to find the crux of the problem before they can "suit the remedy to the case".
For example, after the reservoir dam is completed and filled with water, it often happens that the earthquake activity in the local area and its surrounding areas is intensified due to the change of crustal stress. Fortunately, after the impoundment of the Three Gorges Dam, the local seismic activity did not increase. However, this does not mean that we can rest easy from now on, because the change of crustal stress often has a process. It is worth noting that at the end of 23, a serious blowout occurred in Kaixian natural gas well in Chongqing. The accident was related to the improper operation of workers, but the cause was the increase of crustal stress. At the end of 25, a sudden earthquake occurred in Jiujiang, Jiangxi Province, where there were few earthquakes in history. An earthquake of magnitude 7 caused casualties and property losses. In the summer of 26, there were several earthquakes of magnitude 5 or so in Yanjin and Ludian in Zhaotong, northeast Yunnan. On August 1, 26, 4? An earthquake of magnitude 2. People should pay close attention to the earthquakes that occurred around the Three Gorges Reservoir.
in the summer of 26, the continuous high temperature occurred in Chongqing (the highest temperature was 44? 5 degrees, high temperature weather for more than a month) and a large area of drought; Historical experience shows that if there is abnormal continuous high temperature in a certain area, it may be related to the intensification of surface crustal activity, such as geothermal leakage caused by stress changes in the surface crust, or frictional heat generation effect caused by surface crustal movement. It is worth noting that Chongqing has developed geothermal resources, and there are hot springs in Qijiang, Banan and Beibei, which indicates that there are many ground fissures underground in this geographical area.
At the same time, if the wind resistance effect of the Three Gorges Dam on the Yangtze River reduces the water vapor transport from the downstream to the upstream by one fifth (from the Pacific water vapor); The wind resistance effect of the reservoir dam built on the Jinsha River reduces the water vapor transport from downstream to upstream by one fifth (from Indian Ocean water vapor); Then consider the wind resistance effect of reservoir dams on the tributary water system of the Yangtze River, as well as the wind resistance effect of urban heat islands and urban heat walls in the Yangtze River basin; Then, the total amount of water resources in the Yangtze River may be reduced by about one third (the exact figure needs to be measured). This will not only have a serious impact on the natural ecological environment of the Yangtze River basin, but also on the shipping of the Yangtze River, and will also endanger the survival and development of Shanghai. This is because the reduction of the Yangtze River's water volume will inevitably reduce the amount of sediment transported into the sea by the Yangtze River; However, the decrease in the amount of sediment entering the sea will make Shanghai's coastal areas (including Pudong New Area) and Chongming Island suffer from seawater erosion, which is likely to further evolve into land subsidence and subsidence along the coastal areas. All these are phenomena and problems of related disciplines that artificial terrain climatology needs to pay attention to at the same time.